Hundreds of low-income families could receive new or additional state financial aid following a state Supreme Court decision Tuesday.

The justices ruled unanimously that the state can no longer treat a child’s federal disability assistance as household income when it determines whether the family is eligible for welfare.

Advocates applauded the decision, saying it will return state benefits to families with disabled children who have fallen on hard times and need financial help.

“I’m very, very excited,” said Ruth Heintz, a managing attorney at New Hampshire Legal Assistance, who represented the plaintiffs. “The people that this decision will assist are really the ones who are the poorest of the poor.”

The court ruling overturns a 2014 state rule that governs eligibility for the Temporary Assistance for Needy Families program.

The rule required the state to count a child’s federal Supplemental Security Income payments – meant to assist low-income kids who are blind or severely disabled – as household income. The change disqualified or reduced aid to some New Hampshire families.

Carrie Hendrick, a mother of six, sued the state over the policy in 2014. Hendrick argued SSI money was meant to cover the special needs of her two children who qualify, not provide an income stream for the entire family. After the state rule took effect, Hendrick eventually became ineligible for cash assistance and lost out on nearly $850 a month she had received previously, according to the court ruling.

Jamie Birmingham, a mother of three, later joined the lawsuit. When her child’s SSI payment was counted toward her household income, Birmingham’s family was eligible for $17 a month in cash assistance, according to the court ruling.

The TANF eligibility change came about as a cost- cutting measure approved by the Legislature in 2011. Then, it was projected to save the state roughly $9 million by curbing benefits for an estimated 1,550 cases, according to the bill’s fiscal note.

The Department of Health and Human Services said Tuesday that a preliminary estimate shows 200 SSI recipients over the last five months would have been eligible for additional state assistance under the court ruling.

HHS is now analyzing the court decision’s effect on the TANF program, according to Chief Legal Counsel Frank Nachman. “The ruling will be applied prospectively and the number of families affected will depend on the particular circumstances of each case,” he said in a statement.

The parties will meet in superior court to implement the new ruling, Heintz said.

“We hope that we will be able to work with the DHHS to make that happen in the most efficient way,” she said.

In court proceedings, HHS had argued that the use of an SSI payment for a specific child doesn’t preclude its use for common expenses or its inclusion in the welfare benefit calculation, according to the ruling.

The U.S. Solicitor General argued in an amicus brief, however, that the SSI payment is meant for the sole use of the child, not family expenses. He said the state rule that made SSI benefits available for the whole family “conflicts with federal requirements,” according to the ruling.

The state Supreme Court justices agreed.

Chief Justice Linda Dalianis wrote in the ruling: “Congress intended the SSI program to provide an additional source of federal funds, separate from funds available to needy families with children under the TANF program, to provide disabled children with the minimum amount necessary to satisfy their basic needs.”